The present application is based on and claims under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent Application No. 2000-236010 filed on Aug. 3, 2000 and Japanese Patent Application No. 2001-157080 filed on May 25, 2001, the entire content of both of which is incorporated herein by reference.
The present invention generally relates to variable valve timing systems. More particularly, the present invention pertains to a variable valve timing system for controlling the opening and closing time of an intake valve and an exhaust valve of a vehicle-mounted internal combustion engine.
A known variable valve timing system is described in Japanese Patent Laid-Open Publication No. Hei. 09(1997)-324613. The disclosed variable valve timing system includes a housing member disposed in the driving force transmitting system for transmitting the driving force from the crankshaft of the combustion engine to the camshaft for controlling the opening and closing of either one of the intake valve and the exhaust valve of the combustion engine. The housing member rotates as a unit with one of the crankshaft and the camshaft.
The variable valve timing system also includes a rotor member rotatably assembled on a shoe portion provided on the housing member. The rotor member forms an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member and integrally rotates with one of the camshaft and the crankshaft.
The variable valve timing system further includes a relative rotation controlling mechanism. The relative rotation controlling mechanism allows the relative rotation of the housing member and the rotor member by an unlock operation by the supply of an operation fluid. The relative rotation controlling mechanism restricts the relative rotation of the housing member and the rotor member at an intermediate angle phase between a retarded angle phase and an advanced angle phase by a lock operation by the discharge of the operation fluid. The variable valve timing system still further includes a hydraulic pressure circuit for controlling the supply and discharge of the operation fluid to the relative rotation controlling mechanism as well as for controlling the supply and discharge of the operation fluid to the advanced angle chamber and the retarded angle chamber.
In the aforementioned variable valve timing system, to make the internal combustion engine start in a smooth manner, the open/close timing of one of the intake valve and the exhaust valve is set, under the condition that the relative rotation controlling mechanism restricts the relative rotation between the housing member and the rotor member at a lock phase position within an intermediate region which is located at a position other than the rotation limit ends corresponding to the advanced and retarded angle phase positions, respectively. Thus, at the initial stage of the internal combustion engine, if such the restriction at the lock phase position is not performed, the starting ability of the internal combustion engine may become worse.
With respect to the relative rotation controlling mechanism which restricts the relative rotation between the rotor member and the housing member at the lock phase position, the restriction may be inhibited due to the design of the hydraulic pressure circuit and/or the remaining operation fluid in at least one of the relative rotation controlling mechanism, the advanced angle chamber, and the retarded angle chamber. In addition, in the conventional hydraulic pressure circuit, no consideration has been made as to how to control a hydraulic control pressure valve, which is connected into the hydraulic pressure circuit, upon initiation of the internal combustion engine. This results in the relative rotation phase between the housing member and the rotor member becoming unstable temporally when the internal combustion engine is transferred from its initiation to steady operation condition.
Thus, a need exists for a variable valve timing system for overcoming the aforementioned drawbacks.
In accordance with an aspect of the present invention, a variable valve timing system includes a housing member provided in a driving force transmitting system in which is transmitted a driving force from a crankshaft of an internal combustion engine to a camshaft for controlling opening/closing of one of an intake valve and an exhaust valve of the internal combustion engine, with the housing member rotating together with one of the crankshaft and the camshaft. A rotor member is relatively rotatably assembled on a shoe portion provided on the housing member and forms an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member, with the rotor member rotating together with the other of the camshaft or the crankshaft. A relative rotation controlling mechanism, upon unlock operation thereof established by being supplied with an operation fluid, allows relative rotation between the housing member and the rotor member. The relative rotation controlling mechanism, upon lock operation thereof established by a discharge of the operation fluid therefrom, restricts the relative rotation between the housing member and the rotor member at a lock phase position in an intermediate region located at a position other than the rotation limit ends corresponding to the advanced and retarded angle phase positions, respectively. A hydraulic pressure circuit controls an operation fluid supply/discharge of the relative rotation controlling mechanism and controls an operation fluid supply/discharge of each of the advanced angle chamber and the retarded angle chamber. The hydraulic pressure circuit, upon initiation of the internal combustion engine, discharges the operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers until a pressure of the operation fluid reaches a controllable pressure value. The hydraulic pressure circuit, after the pressure of the operation fluid reaches the controllable pressure value, is adapted to make one of the advanced and retarded angle chambers which is at a superior side of the in phase transfer response characteristic operation fluid filled, is adapted to subsequently make the other of the advanced and retarded angle chambers operation fluid filled, and is adapted to supply the operation fluid to the relative rotation controlling mechanism.
The hydraulic pressure circuit includes a hydraulic pressure control valve in which a control value of the hydraulic pressure control valve is updated, when making one of the advanced and retarded angle chambers which is at the superior side of the in phase transfer response characteristic operation fluid filled, on the basis of a control value for retaining a phase of the relative rotation controlling mechanism while the internal combustion engine is in a steady operation stage before operation of the internal combustion engine is terminated. The control value of the hydraulic pressure control valve can be amended or changed on the basis of the temperature of the operation fluid.
After a time duration has elapsed as measured from the initiation of the internal combustion engine, a decision is made whether or not the pressure of the operation fluid has reached the controllable pressure. The elapse of the time duration is amended depending on one of the temperature of the operation fluid and the revolution number of the internal combustion engine.
A sixth aspect of the present invention is to provide a variable valve timing system whose gist is to modify the structure of the first aspect, wherein switching the supply of the operation fluid from one of the advanced and retarded angle chambers which is at a superior side of in phase transfer response characteristic to the other is established on the basis of a detected value derived from phase detection means. The relative rotation controlling mechanism is made up of a first control mechanism and a second control mechanism, with the first control mechanism restricting the relative rotation in an advancing angle direction upon lock operation at the lock phase position, and the second control mechanism restricting the relative rotation in a retarding angle direction upon lock operation at the lock phase position. The operation fluid is allowed to flow between the hydraulic pressure circuit and the advanced angle chamber by way of the first control mechanism, and the operation fluid is allowed to flow between the hydraulic pressure circuit and the retarded angle chamber by way of the second control mechanism. The hydraulic pressure circuit is capable of being configured to establish that the operation fluid can be controlled by a sole hydraulic pressure control valve.
The hydraulic pressure control valve is adapted to: (1) discharge the operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers when a control current value is zero or minimized; (2) discharge the operation fluid from one of the advanced and retarded angle chambers which is at a superior side of in phase transfer response and supplying the operation fluid to the other when the control current value is at its low level; (3) interrupt the operation fluid supply to and the operation fluid discharge from each of the advanced angle chamber and the retarded angle chamber when the control current value is at its intermediate level; and (4) supply the operation fluid to one of the advanced and retarded angle chambers which is at a superior side of in phase transfer response and discharge the operation fluid from the other when the control current value is at its high level, with the control current value being made high from zero or the minimized level in a short time duration measured from a time when the pressure of the operation fluid becomes equal to or above the value of the controllable pressure.
The hydraulic pressure control valve is also adapted to: (1) discharge the operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers when a control current value is zero or minimized, (2) discharge the operation fluid from one of the advanced and retarded angle chambers and supply the operation fluid to the other when the control current value is at its low level; (3) interrupt the operation fluid supply to and the operation fluid discharge from each of the advanced angle chamber and the retarded angle chamber when the control current value is at its intermediate level; and (4) supply the operation fluid to one of the advanced and retarded angle chambers and discharge the operation fluid from the other when the control current value is at its high level, wherein the control current value is made high temporally such that thereafter the control current value is controlled to a predetermined control current value after the pressure of the operation fluid becomes equal to or above the value of the controllable pressure, when a transfer is made from a first condition to one of a second condition and a third condition, the first condition permitting the discharge of operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers, the second condition making it impossible to supply the operation fluid to and discharge the operation fluid from each of the advanced and retarded angle chambers, and the third condition permitting the discharge of the operation fluid from one of the advanced and retarded angle chambers and the supply of the operation fluid to the other of the advanced and retarded angle chambers.
Upon initiation of the internal combustion engine, in an initial stage of the initiation of the internal combustion, the hydraulic pressure circuit makes it possible to discharge the operation fluid from the advancing angle and retarded angle chambers and the relative rotation controlling mechanism. Thus, the operation fluid remaining in each of the advancing angle and retarded angle chambers can be discharged, resulting in that the remaining operation fluid fails to inhibit or disturb the relative rotation between the rotation member and the housing member, which causes the torque variation in the driving force transmitting system to make it possible to rotate the rotor member quickly relative to the housing member into the lock phase position between the advanced angle phase position and the retarded angle phase positions. In addition, at the initial stage of the internal engine initiation, the remaining operation fluid can be discharged from the relative rotation controlling mechanism, which results in that the lock operation performed therein can be made correct, thereby making it possible to regulate in a relatively precise or correct manner the relative rotation between the housing member and the rotor member at the lock phase position. Thus, the starting ability of the internal combustion engine can be improved.
Upon initiation of the internal combustion engine, in a later stage of the initiation of the internal combustion which comes after the pressure of the operation fluid becomes equal to or greater than the controllable pressure value, after the hydraulic pressure circuit makes one of the advanced and retarded angle chambers which is at the superior side of phase transfer response characteristic operation fluid filled, the other can be made operation fluid filled and the relative rotation controlling mechanism is capable of being supplied with the operation fluid. Thus, while the internal combustion engine transfers its later stage of the initiation operation to a steady operation stage, the relative rotation phase between the housing member and the rotor member can be made to substantially coincide with the lock phase position under the condition that the regulation of the relative rotation control mechanism is released (i.e., the locked state between the housing member and rotor member is released), the relative rotation phase between the housing member and the rotor member can be made stable in an intermediate phase or region.
The variable valve timing system is configured such that the hydraulic pressure circuit includes a hydraulic pressure control valve in which a control value of the hydraulic pressure control valve is updated, when making one of the advanced and retarded angle chambers which is at a superior side of in phase transfer response characteristic operation fluid filled, on the basis of a control value for retaining a phase of the relative rotation controlling mechanism while the internal combustion engine is in normal operation before the internal combustion engine is terminated. Thus, instrumental errors and deteriorations over time can be compensated, which makes it possible to provide constant operation fluid supply characteristics, thereby obtaining a specified operation response characteristic.
The control value of the hydraulic pressure control valve is amended on the basis of the temperature of the operation fluid. In more detail, the opening area of the hydraulic pressure control valve is made smaller (larger) due to lower (higher) viscosity of the operation fluid when the temperature of the operation fluid is high (low). This makes it possible to provide a constant operation fluid supply characteristic freely from the temperature of the operation fluid, thereby obtaining a specified operation response characteristic.
After the elapse of a time duration measured from the initiation of the internal combustion engine, a decision is made whether or not the pressure of the operation fluid reaches the controllable pressure. Thus, detecting whether or not the pressure of the operation fluid reaches the controllable pressure can be made without using a specially prepared hydraulic pressure detecting means.
The elapse of the time duration is amended or changed depending on one of the temperature of the operation fluid and the revolution number of the internal combustion engine. More specifically, making the time duration longer (shorter) when the temperature of the operation is low (high) or when the revolution number of the internal combustion engine is low (high) makes it possible to provide a constant operation fluid supply characteristic freely from the temperature of the operation fluid, thereby obtaining a specified operation response characteristic.
Switching the supply of the operation fluid from one of the advanced and retarded angle chambers which is at the superior side of the in phase transfer responsive to the other is established on the basis of a detected value derived from a phase detection mechanism such as a crank angle detector or cam angle sensors. This makes it possible to establish a switching of the operation fluid at a relative rotation phase in a precise or correct manner, thereby continually obtaining operation response characteristics.
The relative rotation controlling mechanism is made up of a first control mechanism and a second control mechanism, with the first control mechanism restricting the relative rotation in an advancing angle direction upon lock operation at the lock phase position, and the second control mechanism restricting the relative rotation in a retarding angle direction upon lock operation at the lock phase position. The operation fluid is allowed to flow between the hydraulic pressure circuit and the advanced angle chamber by way of the first control mechanism and is allowed to flow between the hydraulic pressure circuit and the retarded angle chamber by way of the second control mechanism so that the hydraulic pressure circuit is capable of being configured to establish control of the operation fluid by a sole hydraulic pressure control valve. Thus, a portion of a flow passage of the operation fluid which extends from the hydraulic pressure circuit to the advanced angle chamber can be used as a flow passage of the operation fluid which extends from the hydraulic pressure circuit to the first control mechanism, while a portion of a flow passage of the operation fluid which extends from the hydraulic pressure circuit to the retarded angle chamber can be used as a flow passage of the operation fluid which extends from the hydraulic pressure circuit to the second control mechanism. Accordingly, the hydraulic pressure circuit can be made much simpler, which results in the hydraulic pressure circuit being capable of being produced in a much smaller size and at a lower cost.
The hydraulic pressure control valve is adapted to: (1) discharge the operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers when a control current value is zero or minimized; (2) discharge the operation fluid from one of the advanced and retarded angle chambers which is at a superior side of in phase transfer response and supply the operation fluid to the other when the control current value is at its low level; (3) interrupt the operation fluid supply to and the operation fluid discharge from each of the advanced angle chamber and the retarded angle chamber when the control current value is at its intermediate level; and (4) supply the operation fluid to one of the advanced and retarded angle chambers which is at a superior side of in phase transfer response and discharge the operation fluid from the other when the control current value is at its high level. The control current value is made high from zero or the minimized level in a relatively short time duration measured from when the pressure of the operation fluid becomes equal or above the value of the controllable pressure. Thus, when the control current shifts from zero or the minimized level (under which the operation fluid can be discharged from the advancing and retarded angle chambers) to the high level (under which the operation fluid can be supplied to one of the advanced and retarded angle chambers which is at the superior side of phase transfer response characteristic, while the operation fluid can be discharged from the other), the time required for such a shift can be minimized.
As a result, even though at the time when the pressure of the operation fluid becomes equal or above the controllable pressure value the operation fluid remains in the advancing and retarded angle chambers and for example the retarded angle chamber is supplied with the operation fluid under the condition that the control current value is at a low level temporally while the control current value shifts from zero or the minimized level to a high level, due to the fact that the condition that the control current value is at a low level temporally lasts for a very small time duration and the amount of operation fluid supplied to the retarded angle chamber is very small, the second control mechanism fails to perform the unlock operation. In the aforementioned temporal period, for example, if the amount of the operation fluid supplied to the retarded angle chamber is large (i.e., the time duration is long during which the control current value takes low level), the supplied operation fluid is added to the remaining operation fluid in the retarded angle chamber, which may make the relative rotation phase between the housing member and the rotor member unstable temporally due to unlock operation of the second control mechanism.
The hydraulic pressure control valve is also adapted to: (1) discharge the operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers when a control current value is zero or minimized; (2) discharge the operation fluid from one of the advanced and retarded angle chambers and supply the operation fluid to the other when the control current value is at its low level; (3) interrupt the operation fluid supply to and the operation fluid discharge from each of the advanced angle chamber and the retarded angle chamber when the control current value is at its intermediate level; and (4) supply the operation fluid to one of the advanced and retarded angle chambers and discharge the operation fluid from the other when the control current value is at its high level. The control current value is made high temporally such that thereafter the control current value is controlled to a predetermined control current value after the pressure of the operation fluid becomes equal to or above the value of the controllable pressure, when a transfer is made from a first condition to one of a second condition and a third condition, with the first condition being made possible to discharge the operation fluid from the relative rotation controlling mechanism and the advanced and retarded angle chambers, the second condition being made impossible to supply the operation fluid to and discharge the operation fluid from each of the advanced and retarded angle chambers, and the third condition being made possible to discharge the operation fluid from one of the advanced and retarded angle chambers and supply the operation fluid to the other of the advanced and retarded angle chambers. Thus, temporally changing the control current value from zero or the minimized level to a high level makes it possible to minimize correctly the time duration during which the control current takes a low level (which shows that the operation fluid can be supplied to and discharged from the retarded angle chamber and the advanced angle chamber, respectively). This results in correct or precise supply/discharge of the operation fluid (e.g., supplying the operation fluid to the advanced angle chamber is made possible, while discharging the operation fluid from the retarded angle chamber is made possible.) and subsequent control of the control current value (e.g., supplying the operation fluid to and discharging the operation fluid from each of supplying the advancing and retarded angle chambers are impossible).